This invention relates generally to the mounting of two bodies, and more particularly the invention relates to the attachment of semiconductor devices to a substrate.
Semiconductor chip cooling requirements are increasing with circuit density, size, and speed. Integrated circuits generating as much as 40 W/cm.sup.2 have been fabricated; power densities as high as 100 W/cm.sup.2 are predicted. Thus, practical cooling of high-power VLSI and ULSI circuits will depend on highly conductive thermal interfaces and chip attachments. Forced air cooling is inadequate for keeping such circuits within safe operating temperatures.
Disclosed in U.S. Pat. No. 4,567,505 is a improved heat sink wherein the heat sink and an integrated circuit are maintained in a low-stress and high-thermal-conductance abutment by pressure from capillary attraction. A surface of one of the two bodies is provided with grooves having reentrant surfaces. A surface of the other both is brought into abutment with the grooved surface, with a liquid therebetween which partially fills the grooves. The grooves act as reservoirs for excess liquid so that a minimum-thickness liquid interface is achieved, and the grooves enable trapped gas to escape out the open ends, thereby preventing a void between the two bodies. Importantly, the groove geometry enforces a well-defined attractive force between the two surfaces due to the liquid surface tension. The grooves in the device surface are formed by chemically etching the surface of the heat sink or the semiconductor substrate. This is satisfactory for bodies such as a wafer of semiconductor material having a smooth planar surface. However, the process is not suitable for materials having rough surfaces or which are not easily etched.